Damper with high dissipating power

ABSTRACT

The invention relates to a shock absorber having high dissipating power and comprising a rod-and-piston assembly ( 12 ) slidably received in a cylinder ( 11 ) and defining on either side of the piston ( 13 ) respective working chambers ( 18; 19 ) containing hydraulic fluid. In the invention, each working chamber ( 18, 19 ) communicates continuously with an associated chamber ( 20, 21 ) containing a heterogeneous energy absorption-dissipation structure constituted by a capillo-porous matrix ( 51, 61 ) and an associated liquid ( 52, 62 ) relative to which the matrix is lyophobic. In addition, each working chamber ( 18, 19 ) communicates with a common compensation chamber ( 30 ) via an associated valve system ( 32, 33 ) including non-return means ( 40, 41 ) ensuring that the working chamber concerned closes automatically during compression, and opens during expansion.

[0001] The present invention relates to a shock absorber with highdissipating power, and more particularly to a shock absorber of the typecomprising a rod-and-piston assembly sliding in a cylinder and definingon opposite sides of the piston respective working chambers containinghydraulic fluid, said rod-and-piston assembly being connected to anexternal source of disturbance and said cylinder being connected to astructure to be protected.

[0002] In conventional shock absorbers, a system comprising a telescopicrod and a return spring is used interposed between the structure to beprotected (e.g. the bodywork of a motor vehicle) and the source ofexternal disturbances (e.g. a wheel of the vehicle that is directly incontact with the ground). A piston rod and cylinder unit is thenprovided which is surrounded by the return spring and which has thefunction of dissipating the energy of the shocks by making use of theviscous flow of the hydraulic fluid. A relationship exists between thefriction force F, the displacement speed {dot over (X)} of the liquid,and its viscosity η (for a Newtonian liquid): the following equationapplies F=G.η ({dot over (X)})^(n) where G is a geometrical factor ofthe solid-liquid system, and n is a power term which generally lies inthe range 1 to 4. Energy is dissipated in conventional shock absorbersby transforming mechanical friction energy in the solid-liquid systeminto heat which is given off to the outside. The amount of energydissipated is proportional to the speed of the movement to the power n,i.e. ΔE=K({dot over (X)})^(n). In particular, in the event ofdisplacement being large and at very low speed (X≈0), then practicallyno energy is dissipated.

[0003] Shock absorber characteristics, as represented by variations inforce as a function of displacement speed, slope to a greater or lesserextent depending on the structure of the shock absorber, and the personskilled in the art knows how to optimize comfort using conventionalmotor vehicle shock absorbers by lowering the characteristic of theshock absorber as much as possible. However, this leads to a paradox inthat in order to have a high degree of energy dissipation andabsorption, it is necessary to have a speed that is high.

[0004] Document GB-A-2 300 892 describes a shock absorber in which eachworking chamber is connected to compliant means, in particular anelastically deformable envelope or a gas spring, or indeed a block ofclosed-cell foam placed in a working chamber. In all circumstances,elastic deformation is used, so the system is reversible and energy isnot dissipated.

[0005] To complete the technological background, mention can be also bemade of document FR-A-85 116 which describes a suspension with variableflexibility, and document FR-A-2 478 763 which describes a hydraulictype energy dissipater.

[0006] The present invention seeks to design a novel type of shockabsorber that is capable of providing a very high degree of energydissipation and absorption, while being structurally lighter in weightand more compact than conventional shock absorbers. It is also desiredthat this novel type of shock absorber should be capable of operatingover a relatively broad band of frequencies, given that a conventionalshock absorber presents a frequency band that generally goes up to 6 Hz.If frequency values in the vicinity of 6 Hz are exceeded, then thevehicle runs the risk of flying over irregularities in the ground thuscausing the wheels to lose adherence with the road.

[0007] According to the invention, this problem is resolved by a shockabsorber having high dissipating power, of the type comprising arod-and-piston assembly slidably received in a cylinder and defining oneither side of the piston respective working chambers containing ahydraulic fluid, said rod-and-piston assembly being connected to anexternal source of disturbance and said cylinder being connected to astructure to be protected, in which:

[0008] each working chamber communicates continuously with an associatedchamber containing a heterogeneous energy absorption-dissipationstructure constituted by at least one capillo-porous matrix and anassociated liquid relative to which said matrix is lyophobic (notwettable); and

[0009] each working chamber also communicates with a common chamber viaan associated valve system, said system including non-return meanscausing the working chamber concerned to close automatically duringcompression, and causing said chamber to open during expansion, saidcommon chamber constituting a compensation chamber ensuring continuityof the hydraulic fluid during displacements of the rod-and-pistonassembly in the cylinder.

[0010] The above-specified concept of a heterogeneous energy dissipatingand absorbing structure using a capillo-porous matrix and an associatedliquid relative to which said matrix is lyophobic is described in detailin the Applicants' document WO-A-96/18040. In that very innovative typeof heterogeneous structure, a solid capillo-porous matrix is used withopen pores and controlled topology, having calibrated passages withvariations in section and/or interconnections so as to form labyrinths,and a liquid surrounding the capillo-porous matrix defining asolid/liquid separation surface, the matrix being lyophobic relative tothe liquid. The separation surface then varies in a manner that isisothermal and reversible as a function of the external pressure towhich the heterogeneous structure is subjected. It is thus possible todefine genuine pairs of capillo-porous solid matrix and matching liquidthat enable quite astonishing energy absorption or accumulationperformance to be obtained (by quasi-reversible isothermal processes)and that enable energy to be dissipated (by irreversible isothermalprocesses) using only the variation in the separation surface in amanner that is quite surprising. The content of the above-specifieddocument is consequently incorporated in the present application byreference.

[0011] Provision can be made for the hydraulic fluid occupying theworking chambers to be identical to the liquid of the heterogeneousenergy absorption-dissipation structures, or in a variant for eachheterogeneous energy absorption-dissipation structure to be confined ina deformable leakproof housing, the hydraulic fluid occupying theworking chambers then being a conventional engineering fluid.

[0012] In a particular embodiment, the rod-and-piston assembly comprisesa rod which is hollow on either side of the piston, each hollow portiondefining internally a chamber containing a heterogeneous energyabsorption-dissipation structure enclosed in a flexible leakproofenvelope.

[0013] In a variant embodiment, the rod-and-piston assembly comprises arod which is solid on either side of the piston, and said shock absorberhas chambers containing respective heterogeneous energyabsorption-dissipation structures enclosed in flexible leakproofenvelopes, which chambers are then placed around the cylinder, inside acommon housing.

[0014] The rod-and-piston assembly of the shock absorber of theinvention can be constituted by two portions having the same outsidediameter, or in a variant by two portions having different outsidediameters, in which case the larger diameter portion is adjacent to thestructure to be protected (e.g. the bodywork of a vehicle), and thesmaller diameter portion is adjacent to the external source ofdisturbance (e.g. the wheel of the vehicle).

[0015] Each flexible leakproof envelope can be secured to the bottom ofthe associated internal chamber of the rod-and-piston assembly or to theinside wall of the common housing, as appropriate, or in a variant itcan be freely suspended in an associated lateral housing rigidly securedto the central housing and in communication therewith via an associatedwindow, or indeed in said associated internal chamber.

[0016] The capillo-porous matrices can be topologically andgeometrically identical on either side of the piston, or in a variantthey can be topologically and geometrically different so as to impart acontrolled amount of asymmetry, and in each case each matrix can besingly-porous or multiply-porous as a function of the stiffness desiredfor the shock absorber.

[0017] Similarly, the lyophobic liquids can have surface tensioncharacteristics which are identical on either side of the piston, or ina variant different on either side so as to impart a controlled amountof asymmetry.

[0018] The common compensation chamber can have a flexible wall so as topresent a volume that is variable. In particular, under suchcircumstances, provision can be made for the flexible wall to surround acentral portion of the cylinder so as to define an annular chamberconstituting the compensation chamber, or for the flexible-walled commoncompensation chamber to be arranged inside the piston which is made tobe hollow, or indeed for the flexible-walled common compensation chamberto be an annular chamber provided at the end of the common housing. In avariant, provision can be made for the common compensation chamber tohave a rigid wall and a bottom that is moving or deformable inassociation with a resilient member (e.g. a volume of gas, a diaphragm,or a piston biased by a spring).

[0019] Preferably, the valve system associated with each working chamberincludes a throttle defining a calibrated orifice for passing hydraulicfluid coming from the common compensation chamber. In particular, eachthrottle is individually adjustable, and in particular can be set to aposition such that the maximum value of the hydraulic resistance of saidthrottle corresponds to the value of the capillary pressure at which theliquid intrudes into the pores of the associated matrix.

[0020] In a particular embodiment, the non-return means of the valvesystem associated with each working chamber comprises a deformable flatcollar with two branches capable of closing radial orifices of thecylinder which communicate via respective channels with the commoncompensation chamber.

[0021] In another particular embodiment, the non-return means of thevalve system associated with each working chamber comprises moving valvemembers optionally biased by associated springs. In particular, themoving valve members may be arranged at the ends of a central tubeopening out into the hollow piston via associated orifices, thecompensation chamber containing a toroidal bellows containing air andsurrounding said tube.

[0022] In which case, it is advantageous for the moving valve members torepresent respective central passages constituting calibrated orifices.

[0023] Other characteristics and advantages of the invention will appearmore clearly in the light of the following description and theaccompanying drawings, relating to a particular embodiment and in which:

[0024]FIG. 1 is a diagrammatic view showing a shock absorber of theinvention with various options for its compensation chamber [A), B), C)]and for its heterogeneous energy absorption-dissipation structure [a),b), c)];

[0025]FIG. 2 is an axial section of a particular shock absorberstructure of the invention;

[0026]FIG. 3 is a fragmentary section on a larger scale of the aboveshock absorber;

[0027]FIG. 4 is a section associated with line IV-IV in FIG. 3;

[0028]FIG. 5 is a detail view in section on a larger scale showing moreclearly the structure of the valve system associated with each workingchamber of the shock absorber;

[0029]FIG. 6 is a fragmentary section view of the above shock absorberwith the rod-and-piston assembly and the flexible leakproof envelopecontaining a heterogeneous energy absorption-dissipation structure beingcut away so as to show more clearly how the non-return means forming apart of the associated valve system are arranged;

[0030]FIG. 7 is a perspective view showing the structure of the abovenon-return means;

[0031]FIG. 8 is a graph showing various characteristics of a shockabsorber of the invention using multiply-porous matrices, the variouscurves resulting both from the throttling system being opened todifferent extents as shown in FIG. 8a and from various different matrixstructures as shown in FIG. 8b, which are curves showing the pore sizedistributions of the matrices;

[0032]FIG. 9 is a graph showing various characteristics of a shockabsorber of the invention using singly-porous matrices, as representedby the graph of associated FIG. 9a;

[0033]FIGS. 10 and 11 show the characteristics of a shock absorber ofthe invention for the shock and the rebound portions thereof;

[0034]FIG. 12 is a diagram showing both the static characteristic of theshock absorber of the invention and that of a conventional shockabsorber, said diagram revealing the high energy absorption power of theshock absorber of the invention compared with conventional systems;

[0035]FIG. 13 is a diagram showing another feature of the shock absorberof the invention, in which the force F does not vary with displacementspeed below a critical speed;

[0036]FIG. 14 shows the characteristic of the shock absorber of theinvention built up point by point at different speeds (in the range 5millimeters per second (mm/s) to 200 mm/s;

[0037]FIG. 15 is another characteristic diagram obtained by varyingfrequency over the range 1 Hz to 12 Hz, said diagram showing that forceF is independent of frequency below the critical speed;

[0038]FIG. 16 is a diagram showing the characteristics of a liquid andlyophobic matrix pair at different speeds for the shock absorber rod,including zero speed (0 to 5 meters per second (m/s)), said diagramshowing that the pressure P (or the force F) is independent of speed(where the speeds in question are below the critical speed);

[0039]FIGS. 17 and 18 are sections through two other variant embodimentsof a shock absorber of the invention, with a rod-and-piston assembly inwhich the rod and the piston are hollow;

[0040]FIG. 19 is a section through yet another variant embodiment, witha rod-and-piston assembly whose rod is solid and with peripheralchambers receiving the heterogeneous energy absorption and dissipationstructures;

[0041]FIG. 20 is a section on XX-XX of FIG. 19 showing the peripheralworking chambers more clearly;

[0042]FIG. 21 is a fragmentary view showing detail XXI of FIG. 19relating to the vicinity of a check valve, on a larger scale;

[0043]FIG. 22 is a section view through another variant derived fromthat of FIGS. 19 to 21 in which each flexible envelope is received in alateral housing rigidly secured to the central housing which isassociated with the rod-and-piston assembly; and

[0044]FIG. 23 is a section on XXIII-XXIII of FIG. 22 showing moreclearly how the two lateral housings are arranged.

[0045] The general structure of a shock absorber of the invention isdescribed initially with reference to FIG. 1.

[0046] There can be seen a shock absorber referenced 1 which is of thetype comprising an assembly comprising a rod 2 and a piston 3 slidablyreceived in a cylinder 4 and defining on either side of the piston 3respective working chambers 5.1 and 5.2 containing hydraulic fluid. Therod-and-piston assembly 2, 3 is connected to an external source ofdisturbance SP (e.g. a motor vehicle wheel in contact with the ground),while the cylinder 4 is connected to a structure to be protected S (e.g.the bodywork of the vehicle). The end of the rod connected to theexternal source SP moves axially with displacement X(t) and transmits aforce F(t), where the parameter t is time.

[0047] According to a first essential characteristic of the invention,each working chamber 5.1, 5.2 is permanently in communication with anassociated chamber 6.1, 6.2 containing a heterogeneous energyabsorption-dissipation structure constituted by at least onecapillo-porous matrix 9 and an associated liquid 9′ relative to whichthe matrix is lyophobic (i.e. the liquid 9′ does not wet the porousmatrix 9). Such a pair comprising a capillo-porous matrix and anassociated non-wetting liquid is described in detail together with theprinciple whereby said heterogeneous structure operates inabove-mentioned document WO-A-96/18040.

[0048] By way of non-limiting example, the porous matrices can be madeof the following materials: silicagels; alumino-silicates; all types ofzeolites; porous glasses, . . . ; and the associated non-wetting liquidscan be as follows: water; aqueous solutions; low temperature eutetics;polar liquids; . . . .

[0049] In the example a), the hydraulic fluid occupying the workingchambers 5.1, 5.2 is identical to the liquid 9′ in the heterogeneousenergy absorption-dissipation structures to be found in the chambers6.1, 6.2: in this case there is only one type of fluid.

[0050] In general, it is preferable for each heterogeneous structure 9,9′ to be confined in a deformable leakproof housing as shown in examplesb) and c), with the hydraulic fluid occupying the working chambers 5.1,5.2 then being a conventional engineering fluid such as oil. In b), theleakproof housing is defined by a diaphragm 6′.1 and in c) by a bellowsenvelope 6″.1.

[0051] According to a second essential characteristic of the invention,each working chamber 5.1, 5.2 also communicates with a common chamber 7via an associated valve system 8.1, 8.2. Each valve system includesnon-return means 8.11, 8.21 which ensures that the corresponding workingchamber 5.1, 5.2 closes automatically during compression, and opens saidchamber during expansion.

[0052] The common chamber 7 constitutes a compensation chamber whichensures continuity of the hydraulic fluid contained in the workingchambers 5.1, 5.2 during displacement of the rod-and-piston assembly 2,3 in the cylinder 4.

[0053] Each valve system 8.1, 8.2 preferably also includes an adjustablethrottle 8.12, 8.22 defining a calibrated through orifice.

[0054] Specifically, the common compensation chamber 7 has a rigid walland is disposed outside the cylinder 4, but that is not essential asexplained below.

[0055] The common compensation chamber 7 has a moving or deformable endwall associated with a resilient member. Three possible variants areshown here: at A) the moving end wall is a flexible diaphragm 71 and theresilient member is a volume of compressed air 7′.1; at B) the movingend wall is a piston 7″ and the resilient member is a spring 7″.1; andat C) the moving end wall is a flexible diaphragm 7″ ′ having a rigidcentral disk, and the resilient member is a spring 7″ ′.1.

[0056] The operation and the advantages of such a shock absorber aredescribed below with reference to FIG. 2 which shows a completeembodiment of the shock absorber of the invention in a more structuralmanner.

[0057] The structure of a shock absorber of the invention is describedin greater detail below with reference to FIGS. 2 to 7, for a firstembodiment thereof.

[0058]FIG. 2 shows a shock absorber referenced 10, of the typecomprising a rod-and-piston assembly 12 sliding in a cylinder 11 anddefining respective working chambers 18, 19 on opposite sides of thepiston 13, which chambers are in permanent communication with associatedinternal chambers 20, 21 inside the rod-and-piston assembly 12.

[0059] Specifically, the rod-and-piston assembly 12 is constituted bytwo hollow portions 14 and 15 having the same outside diameter,extending on opposite sides of the piston 13, sealing is provided byassociated O-rings 16, 17. The rod-and-piston assembly 12 then slides inan axial direction 100 inside the cylinder 11 on an axis D, the end 14.1of the rod-and-piston assembly being connected to an external source ofdisturbance (not shown here). When mounted on a motor vehicle, thisportion 14.1 is preferably associated with the wheel of the vehicle, andthe opposite portion 11.1 of the cylinder 11 having an extension forminga protective cap 11.2 at its end is associated with the structure to beprotected, e.g. the bodywork of said vehicle.

[0060] As explained below for the variants shown in FIGS. 17 to 23,provision can be made for the rod-and-piston assembly 12 to beconstituted by two portions that are of different outside diameters, inwhich case it is advantageous to provide for the larger diameter portionto be disposed adjacent to the structure to be protected and the smallerdiameter portion adjacent to the external source of disturbance so as toabsorb shock with minimum force (improving passenger comfort in thevehicle), and so as to exert a rebound with a greater force (improvingwheel adherence on the road).

[0061] It can be seen that each internal chamber 20, 21 of therod-and-piston assembly 12 communicates via associated orifices 14.3,15.3 with the associated working chamber 18, 19 which corresponds inthis case to the annular space defined between the body of the cylinder11 and the outside surface of the rod-and-piston assembly 12.

[0062] According to the above-mentioned first essential characteristicof the invention, each internal chamber 20, 21 of the rod-and-pistonassembly 12 contains a flexible leakproof envelope 50, 60 itselfcontaining a heterogeneous energy absorption-dissipation structureconstituted by a capillo-porous matrix 51, 61 and an associated liquid52, 62 relative to which said matrix is lyophobic. As mentioned above,such a pair comprising a capillo-porous matrix and an associatednon-wetting liquid is described in detail together with the principlewhereby the heterogeneous structure operates in the above-mentioneddocuments WO-A-96/18040. It should be observed that the liquid 52, 62contained in leakproof manner in the associated envelope 50, 60 hasnothing to do in this case with the hydraulic fluid that occupies theinternal chambers 20 and 21 of the rod-and-piston assembly 12 and theassociated working chambers 18, 19, which hydraulic fluid is aconventional engineering fluid such as oil.

[0063] In this case, each flexible leakproof envelope 50, 60 is securedto the end wall 14.2, 15.2 of the associated internal chamber 20, 21 ofthe rod-and-piston assembly 12. Collars 14.4 and 15.4 are showndiagrammatically projecting from the end wall 14.2, 15.2 of therod-and-piston assembly 12, which collars are connected to the open endsof the associated flexible envelopes, fastening being achieved by meansof clamping collars 14.5, 15.5.

[0064] Although not shown herein, in a variant, it would be possible toprovide for each flexible leakproof envelope 50, 60 to be freelysuspended inside the associated internal chamber 20, 21 of therod-and-piston assembly 12.

[0065] The capillo-porous matrices 51, 61 contained within theirflexible leakproof envelopes 50, 60 are generally topologically andgeometrically identical on either side of the piston 13. Nevertheless,it would be possible in a variant to provide for the capillo-porousmatrices 51, 61 to be topologically and geometrically different onopposite sides of the piston 13, thereby deliberately imparting apredetermined amount of asymmetry. In this case, for example, ifdifferent geometries are selected (different radii for the pores and thecapillaries), then the matrix having the smaller radius pores andcapillaries is placed in the chamber that is associated with rebound (soas to have a high force on this side of the piston), while the matrixhaving the pores and capillaries of larger radius is placed in thechamber which is associated with shock. Naturally, it would also bepossible to modify the topology of the pore space in the two matrices.

[0066] In order to obtain such a predetermined amount of asymmetry, itis possible in a variant to use capillo-porous matrices that areessentially identical (topologically and geometrically) on either sideof the piston 13, but to have these matrices immersed in liquids thatpresent different surface tension characteristics on either side of saidpiston. Under such circumstances, the liquid having the higher surfacetension is placed in the chamber associated with rebound (in order tohave a higher force on this side of the piston), and the liquid withlower surface tension is placed in the chamber which is associated withshock.

[0067] In both cases, each capillo-porous matrix 51, 61 can besingly-porous or multiply-porous depending on whether the distributionfactor for pores of radius r within the volume V of the matrix is zeroor non-zero, respectively. This factor can be written ∂r/∂V where∂r/∂V=0 for a singly-porous matrix and ∂r/∂V≠0 for a multiply-porousmatrix. These structural features of capillo-porous matrices aredescribed in detail in the above-mentioned document WO-A-96/18040.

[0068] It is known that with such heterogeneous structures, the liquidsurrounding the capillo-porous matrices penetrates into the pores ofsaid matrices only when the surrounding liquid pressure exceeds theso-called Laplace pressure, which capillary pressure is given by theformula P=(2σ·|cos θ|)/r where σ is the surface tension of the liquidused, θ is the solid-liquid angle of contact (in this case much greaterthan 90°), and r is the radius of the capillary pores in the porousmatrix (r in this case lies between the radius of the molecules of thenon-wetted liquid used, and a value of about one-tenth of a micrometer).It is this fundamental formula which governs the pressure that prevailsin the heterogeneous system, i.e. inside each leakproof flexibleenvelope 50, 60.

[0069] The combined use of capillarity phenomena and Pascal's law forhydraulic systems (pressure is identical at all points within a closedspace) ensures that the pressure inside the envelope 50, 60 is identicalto the pressure inside the chambers 18, 20 and 19, 21, respectively.Furthermore, in order to enable the shock absorber to operate, thevolume of liquid in the envelopes 50, 60 must be not less than the sumof the volumes of the pores in the corresponding matrix plus the volumesbetween the porous particles of said matrix.

[0070] According to the above-mentioned second essential characteristicof the invention, each working chamber 18, 19 also communicates with acommon chamber via an associated valve system, said system includingnon-return means for closing the corresponding working chamber duringcompression, and opening said chamber during expansion. This commonchamber constitutes a compensation chamber that ensures continuity forthe hydraulic fluid during displacements of the rod-and-piston assembly12 in the cylinder 11.

[0071] In this case, the common compensation chamber referenced 30 has aflexible wall (wall 31) so as to be variable in volume. The flexiblewall 31 surrounds a central portion of the cylinder 11 so as to definean annular chamber constituting the compensation chamber 30. Theconnections between the compensation chamber 30 and the working chambers18, 19 take place via respective channels 28, 29 leading to theassociated valve systems 32, 33, and respective pluralities of channels22, 23 (six channels in each case) connecting with a terminalcompartment 18.1 or 19.1 of the working chamber 18, 19.

[0072] As mentioned above, it is possible in a variant to provide acommon compensation chamber having a rigid wall, in which case it wouldbe outside the shock absorber, and connected to the working chambers 18,19 via associated pipes, the common compensation chamber then presentinga moving or deformable end wall associated with a resilient member.Under such circumstances, the common compensation chamber having a rigidwall communicates with each working chamber 18, 19 via a respectivevalve system identical to that described below.

[0073] In practice, it is preferable for the compensation chamber tohave a flexible wall if the system is to remain in a low frequency range(return flows are driven by the difference between atmospheric pressureand the suction in the working chambers during expansion), and a rigidwall if the system remains in a high frequency range.

[0074] As shown in FIGS. 2 and 3, the valve system 32, 33 associatedwith each internal chamber 20, 21 of the rod-and-piston assembly 12includes a throttle 34, 36 defining a calibrated orifice 26, 27 forpassing the hydraulic fluid coming from the common compensation chamber30 via the link channels 28, 29. Specifically, each throttle 34, 36 ismounted on an associated projection 35, 37 from the cylinder body 11.The distal end of each throttle 34, 36 has a conical endpiece 38, 39co-operating with a calibrated orifice 26, 27 to define a predeterminedwidth. Preferably, as shown herein, each throttle 34, 36 is individuallyadjustable from the outside, which can be achieved in this case bytightening or loosening a threaded portion of the throttle in a boreassociated with the projection 35, 37. This makes it easy to achieve anyparticular adjustment for the shock absorber as a function of theconditions encountered, as described in greater detail below. Inparticular, arrangements can be made for the position of each throttle34, 36 to be set to a value such that the maximum value of the hydraulicresistance of said throttle corresponds to the capillary pressure valueat which the liquid 52, 62 intrudes into the pores of the associatedmatrix 51, 61 (Laplace capillary pressure).

[0075] The valve system 32, 33 associated with each internal chamber 20,21 also has non-return means implemented in this case in the form of adeformable flat collar 40, 41 disposed in the associated terminalcompartment 18.1, 19.1. As can be seen more clearly in FIGS. 4 to 7,each deformable flat collar 40, 41 has two branches that can closeradial orifices 24, 25 of the cylinder 11 communicating via the sixrespective channels 22, 23 with the common compensation chamber 30.

[0076] FIGS. 4 to 7 show more clearly how the flat collar 40 associatedwith the working chamber 18 is implemented, but it should be understoodthat the other collar 41 which is associated with the other workingchamber 19 is identical in structure.

[0077] The collar 40 (FIGS. 4 to 7) is made of beryllium bronze, forexample, thus presenting two flat branches 40.1 extending from astationary top portion 40.4 (FIG. 7). Fingers 40.2 and 40.3 are bondedthereto to hold the deformable collar 40 in position in the associatedhousing 18.1. In FIGS. 6 and 7, the width of compartment 18.1 isreferenced l. The fingers 40.2 associated with the stationary portion40.4 of the collar 40 are slightly longer than l, referenced herein asl+ε so as to hold the collar 40 in place by wedging. In contrast, theother fingers 40.3 are slightly shorter, written l−ε, so as to leave thebranches 40.1 of the collar 40 free to move transversely inside thecompartments 18.1 and 19.1. It will readily be understood that thebranches 40.1 are naturally pressed by the resilience of the collar 40against the orifices 24 of the channels 22, thereby closing saidchannels. However, if hydraulic fluid coming from the compensationchamber 30 arrives via the channels 22, this fluid can exert sufficientthrust to move the branches 40.1 of the collar 40 towards each otherthus allowing the fluid to pass through the orifices 24.

[0078] In the detail of FIG. 5, there can be seen a washer 41 havingorifices 42 serving both to hold the collar 40 in position and to allowthe fluid arriving via the calibrated orifice 38 to pass through. Thisconstitutes a variant embodiment having the advantage of simplifyingmanufacture of the flat collar, and in particular of avoiding the needto bond the holding fingers thereto.

[0079] The operation and the characteristics of the shock absorber ofthe invention made structurally as described above with reference toFIG. 2 are described below in greater detail with reference to FIGS. 8to 16.

[0080] Initially the situation of the shock absorber at rest isexamined, i.e. when it is not subjected to any external stress. Therod-and-piston assembly 12 (FIG. 2) is then in mutual equilibrium, withsaid rod-and-piston assembly being located, for example, in the middleof the cylinder 11 due to action from an external return spring (notshown), it being understood that the assembly can be stopped in anarbitrary position. The pressures in the two working chambers 18, 19 andalso in the compensation chamber 30 are then all equal. The pore spacesin the matrices of the heterogeneous structures enclosed in theenvelopes are then empty, with this being the result of the fact thatthe associated liquid cannot spontaneously penetrate into the capillarypores of the matrices because they are not wettable by said liquid(angle θ considerably greater than 90°). Thus, even in the absence of areturn spring, a certain amount of force must be applied to therod-and-piston assembly in order to move the piston. This means that inequilibrium the position of the piston is automatically determined, suchthat self-stabilization is obtained that is most advantageous inpractice since it prevents the system being rigid.

[0081] If the shock is now exerted on the free end of the rod-and-pistonassembly 12, tending to displace the assembly to the right in FIG. 2,the throttle 36 behaves as a plug and prevents the hydraulic fluid inthe working chamber 19 from going towards the compensation chamber 30,and the check valve 41 is closed so that the chambers 19 and 21 form aclosed receptacle. The quasi-condensed fluid compresses the flexibleenvelope 60 and the pressure inside said envelope increases from thevalue of atmospheric pressure, such that once the pressure exceeds thevalue of the Laplace capillary pressure, the volume inside the envelope60 is decreased as the working liquid 62 penetrates into the pores ofthe associated porous matrices 61. In parallel with the increase inpressure (compression) in the chambers 19 and 21, there is a decrease inpressure (expansion) in the other chambers 18 and 20. The presence ofthe check valve 40 and of the compensation chamber 30 serves to preventa vacuum appearing in the chambers 18 and 20, thus ensuring that thecondensed phase remains continuous.

[0082] Because of the two throttles 34, 36 which are adjustable, it ispossible to set the determined hydraulic resistance that needs to beovercome by liquid being driven between the chambers 18, 20 and 19, 21through the compensation chamber 30. In this case, the pressure to beovercome is the capillary pressure at which the lyophobic liquidintrudes into the associated matrices (the Laplace capillary pressure).

[0083] Returning now to the piston moving to the left in a dynamicstate, it can be seen that the volume of the heterogeneous system in thecompression chamber 18 diminishes under the action of the forcedcompression pressure (due to external action). Simultaneously with thisphenomenon in the chambers 18 and 20, the hydraulic fluid is deliveredfrom the compensation chamber 30 to the chamber 19, 21 via the checkvalve 41 so as to ensure that the condensed phase remains continuous inthe space provided by the chambers 19, 21. If the rod-and-pistonassembly stops at some moment and thereafter is urged to begin to movein the opposite direction, then forced compression occursinstantaneously in the chamber 19, 21 because of the hydraulicresistance of the throttle 36, and the liquid intrudes into thecapillary pores of the heterogeneous system contained in the envelope60, while simultaneous expansion occurs in the chambers 18 and 20 withthe liquid being expelled spontaneously from the capillary pores of theheterogeneous system contained in the envelope 50. During this expansionof the heterogeneous system, the volume of the envelope 50 increases,occupying the space of the chamber 20. If at this moment there is adeficit in the volume of condensed fluid in the chamber 18, 20, thefluid in the compensation chamber 30 will penetrate via the check valve40 into the space of the working chambers 18 and 20 under drive from thepressure difference (atmospheric pressure acting on the flexible wall 31plus possible suction in the internal chamber 20) as the rod-and-pistonassembly moves to the right.

[0084] In other words, independently of the position and of the traveldirection of the piston 13 (FIG. 2), the heterogeneous system is readyat all times to absorb the energy of the external shock or the reboundenergy in the corresponding working chamber so as to dissipate it in theopposite working chamber. The compensation chamber 30 is fundamentalsince it serves to provide hydraulic fluid continuity in the system,preventing any rupture that could arise either from thecompression/expansion speed or from geometrical asymmetry as mightresult, for example, from a difference in the diameters of the twoportions of the hollow rod 12.

[0085] With reference now to the graph of FIG. 8, which corresponds tomultiply-porous matrices, it can be seen that variations in force F as afunction of displacement speed {dot over (X)} have a first speed zone Z1which could be referred to as being “Newtonian”, followed by a secondzone Z2 which corresponds more particularly to the operation of thecorresponding lyophobic heterogeneous system. The various linearportions referenced A, B, and C in the zone Z1 correspond, in fact, tothe throttle 34 being opened to different degrees, as representeddiagrammatically in FIG. 8a, having a maximum value A, a medium value B,and a minimum value C. For the zone Z2, the characteristics are ofdifferent slopes as a function of the geometry and shape of themultiply-porous matrix. With reference to FIG. 8b which shows three poresize distribution curves (in terms of radius r) for the matrices in thevolume V, it can be said that the segments A1, B1, C1 correspond to arelatively sharp distribution curve of the type M1, while the curves A2,B2, C2 correspond to a medium distribution of the type M2, and thecurves A3, B3, C3 correspond to a flatter distribution M3. The segmentsA3, B3, C3 correspond to the shock absorber being on a hard setting,while the segments A2, B2, C2 correspond to a medium setting and thesegments A1, B1, C1 correspond to a comfortable setting. The horizontalsegments A0, B0, C0 correspond to an ideal setting, of a kind that isnever achieved in practice.

[0086] Under such circumstances, use is made both of adjustments to thethrottle and of a suitable choice for the geometry/morphology of theporous matrices in the heterogeneous structure for the purpose ofadjusting the characteristics of the shock absorber as a function of theconditions encountered. The liquid with respect to which the porousmatrices are lyophobic remains essentially invariable (FIG. 8).

[0087] The graph of FIG. 9 shows behavior with a singly-porous matrix(r₀=constant). Adjustments to the throttle then define a first portionof the characteristic that slopes at a different angle depending on howopen the throttle is (max, medium, min) together with a correspondingextent for the “Newtonian” zone Z1. Thereafter the force F ispractically constant, i.e. it does not depend significantly on speed{dot over (X)}. This illustrates a quite remarkable feature of the shockabsorber of the invention setting it well apart from conventional shockabsorbers which have a characteristic where force is proportional todisplacement speed to a power of at least 1. FIG. 9a is a simple diagramshowing the distribution of pore sizes in the volume V, it beingrecalled that this is a singly-porous matrix, i.e. it has a pore radiusr set on the value r₀ (e.g. a molecular sieve, zeolites, . . . ).

[0088] The diagrams of FIGS. 10 and 11 show characteristics comprisingboth rebound and shock as obtained with a shock absorber of theinvention, with a force that is constant as from when the heterogeneousstructures start to work, respectively with singly-porous matrices andwith multiply-porous matrices.

[0089] The diagram of FIG. 12 shows both the behavior of a shockabsorber of the invention (solid line curve plotting force F as afunction of displacement ΔX) and the behavior of a conventional shockabsorber (chain-dotted line). With conventional shock absorbers, havingcharacteristics in which F is proportional to {dot over (X)}, thedisplacement ΔX can be represented in FIG. 12 as being ΔX={dot over(X)}.Δt (where Δt is a unit time interval). It can be seen that theshaded zone associated with conventional shock absorbers corresponds tomuch less dissipation of energy than that associated with a shockabsorber of the invention. If the ratio of energy dissipated overworking chamber volume is calculated, which ratio corresponds tocapacity for dissipation, it can be seen that the shock absorber of theinvention makes it possible to obtain a capacity for dissipation that is100 to 1000 times greater. Performance is thus obtained which is quiteremarkable in terms of the amount of energy dissipated while using avery small volume of working liquid.

[0090] The plot of FIG. 13 (force F as a function of displacement speed{dot over (X)}) shows that the force F does not vary with displacementspeed so long as the speed remains below a critical speed {dot over(X)}_(c) (isothermal conditions for the compression/expansion cycle ofthe lyophobic heterogeneous structure). Above the critical {dot over(X)}_(c), the force F increases with speed {dot over (X)}: this can beexplained by the deficit of heat flux coming from the outside to thecompression chamber relative to the heat flux necessary for isothermalformation of the matrix/liquid interface which is normally endothermic.When {dot over (X)}>{dot over (X)}_(c), the process approximates aprocess that is quasi-adiabatic, thereby reducing the temperature of theheterogeneous system and increasing surface tension (and thus theLaplace capillary pressure). The Laplace pressure determines the force Fwhich therefore increases on the plot of FIG. 13.

[0091] The plot of FIG. 14 (force F as a function of absolutedisplacement ΔX) needs to be compared with that of FIG. 12, and is builtup point by point for different displacement speeds {dot over (X)} inthe range 5 mm/s to 200 mm/s), with the points all remaining on the samecurve regardless of speed (providing it is below the above-mentionedcritical speed).

[0092] The plot of FIG. 15 (force F as a function of displacement {dotover (X)}) shows values measured at different frequencies (1 Hz, 3 Hz, 6Hz, 9 Hz, and 12 Hz): it can be seen that the force F is independent offrequency below the critical speed {dot over (X)}_(c).

[0093] The plot of FIG. 16 (pressure P as a function of variation involume ΔV, or indeed force F as a function of displacement ΔX) shows aplurality of characteristics measured at different speeds for the rod ofthe shock absorber, including zero speed (0 m/s or static, 1 m/s, 2 m/s,2.5 m/s, 3 m/s, 3.5 m/s, 4 m/s, 4.5 m/s, and 5 m/s). It can be seen thatthe pressure P (or the force F) is practically independent of speed (thespeeds in question all being lower than the critical speed), such thatthe dynamic characteristic remains, in practice, practically identicalto the static characteristic. It can be seen that variation in pressurevaries by only a few percent even though the variation in speed between0 and 5 m/s is proportionally very large.

[0094] It is clear that the characteristics of the shock absorber of theinvention as shown on the above plots are quite unlike those ofconventional shock absorbers.

[0095] Other structural variants of the shock absorber as describedabove are described briefly below with reference to FIGS. 17 to 23.

[0096] In FIG. 17, corresponding members are given the same referencesas before plus 100.

[0097] The structure of FIG. 17 differs from that of FIG. 2 in that eachflexible leakproof envelope 150, 160 is freely suspended in theassociated internal chamber 120, 121 of the rod-and-piston assembly 112,and above all by the fact that the common compensation chamber 130having a flexible wall 131 (a bellows of metal or of plastics materialcontaining air) is arranged inside the piston 113 which is made hollowfor this purpose. The compression chambers 118, 119 communicate with thespace surrounding the envelopes 150, 160 via windows 114.3, 115.3. Equalpressure hydraulic communication in the static state is provided oneither side of the piston by moving valve members 132, 133 biased byrespective blade springs 132′, 133′, each valve member also having acentral orifice 138, 139 forming a constant calibrated orifice (i.e. notadjustable in this case). Since the portions 114, 115 of the hollow rodare of different diameters, the rebound force is greater than the shockforce (written F_(r)>F_(ch)).

[0098] In FIG. 18, the references have been increased by a further 100.The difference compared with the variant of FIG. 17 lies incommunication with the compensation chamber 230: a central tube 232′ isused whose ends are suitable for being closed by means of floating valvemembers 232, 233 each having a calibrated central passage 238, 239 andopening out via middle orifices 232″ into the chamber 230. The flexibleenvelope 231 which is in the compensation chamber 230 contains air asabove, but it is now arranged in the form of a toroidal bellowssurrounding the central tube 232′. As mentioned above, F_(r)>F_(ch).

[0099] The solution of FIG. 18 is more advantageous than that of FIG. 17when there is very little annular room available for receiving the checkvalves 132, 133 (FIG. 17) outside the portions 114, 115.

[0100] In FIGS. 19 to 23, the references are increased by a further 100.The rod-and-piston assembly 312 then has a rod which is solid on eitherside of the piston 313. The shock absorber 310 then has two chambers320, 321 which are arranged around the cylinder 311, inside a commonhousing 370 (the variant of FIGS. 19 to 21). These two chambers 320, 321are defined by radial webs 375 and each contains a heterogeneousstructure 351, 352 and 361, 362 contained inside an associated flexibleleakproof envelope 350, 360.

[0101] Each flexible leakproof envelope 350, 360 is then secured to theinside wall of the common housing 370.

[0102] The common compensation chamber 330 having a flexible wall 331(metal or plastics bellows) is an annular chamber arranged in anextension 371 of the common housing 370, and is closed by a cover 372.

[0103] Communication with the compensation chamber 330 is provided bymoving check valves 332, 333 biased by a spring 332′ (only one can beseen in the detail of FIG. 21), each check valve having a centralpassage 338, 339 forming a calibrated orifice.

[0104] Again the relationship F_(r)>F_(ch) applies (because the twosegments of the solid rod are of different diameters).

[0105]FIGS. 22 and 23 show a variant of the preceding embodiment asshown in FIGS. 19 to 21. This variant differs from the preceding variantin that the envelopes 350, 360 are housed in two lateral housingsreferenced 370.1, 370.2 which are rigidly secured to the central housing370 associated with the rod-and-piston assembly 313. Communicationbetween the lateral housings 370.1, 370.2 and the central housing 370continues to be provided via common windows 314.3, 315.3 (shown insection in FIG. 23). The advantage of such an arrangement lies instructural implementation being simplified: it is easier to make thefour external welds associated with the lateral housings 370.1, 370.2than to make the eight internal welds associated with the radial webs375 in the preceding variant. In addition, the envelopes 350 and 360 canbe made in the form of elongate tubes, thus making them easier tomanufacture and simpler to secure inside their respective chambers.

[0106] Finally, a shock absorber has been made in this manner having avery high degree of energy dissipation, i.e. of the order of 90% to 95%,whereas conventional shock absorbers can only reach values thatgenerally lie in the range 30% to 40% under the best of circumstances.

[0107] In addition, it is shown above that the force applied to therod-and-piston assembly of the shock absorber can remain independent ofits displacement speed over certain speed ranges. This property whichhas never been obtained before with conventional shock absorbers canprovide good comfort for the passengers of a vehicle. With the help ofthrottles, it is possible to ensure a linear relationship between forceand speed over a low speed range. The procedure for adjusting thethrottles to reach the speed zone concerned consists in varying thethrough section for the hydraulic fluid so that the maximum value of thehydraulic resistance of the throttle is equal to the capillary pressurethat ensures the liquid can intrude into the pore space of the matricesin the heterogeneous structure that is placed in the flexible envelopes.In the range of speeds beyond a critical threshold, the force becomesdependent on displacement speed. The heterogeneous systems then act asfilters for external disturbances providing excellent comfort for thepassengers of the vehicle, and also diminishing the forces on saidvehicle as a whole.

[0108] It is also possible to obtain a shock absorber which is 30% to40% lighter than conventional shock absorbers and 30% to 40% morecompact (1500 cm³ for the volume of homogeneous fluid (oil) in theworking chambers of a conventional shock absorber, to be compared with12 cm³ to 15 cm³ for the volume of heterogeneous fluid in a shockabsorber of the invention).

[0109] Finally, the shock absorber of the invention makes it possible toenvisage operating over a frequency range going up to 30 Hz and beyond,whereas a conventional shock absorber generally becomes ineffectivebeyond 6 Hz.

[0110] The invention can be applied to a very wide variety of fields,and by way of non-limiting example, mention can be made of motorvehicles, rail vehicles, railway bumpers, aircraft landing gear, enginesupports, various anti-vibration protection devices (including againstsoundwaves), anti-earthquake systems, and couplings between spacemodules.

[0111] The invention is not limited to the embodiment described above,but on the contrary covers any variant that uses equivalent means toreproduce the essential characteristics specified above.

1. A shock absorber having high dissipating power, of the typecomprising a rod-and-piston assembly (2, 3) slidably received in acylinder (4) and defining on either side of the piston (3) respectiveworking chambers (5.1; 5.2) containing a hydraulic fluid, saidrod-and-piston assembly being connected to an external source ofdisturbance (SP) and said cylinder being connected to a structure to beprotected (S), the shock absorber being characterized in that: eachworking chamber (5.1; 5.2) communicates continuously with an associatedchamber (6.1; 6.2) containing a heterogeneous energyabsorption-dissipation structure constituted by at least onecapillo-porous matrix (9) and an associated liquid (9′) relative towhich said matrix is lyophobic; and each working chamber (5.1; 5.2) alsocommunicates with a common chamber (7) via an associated valve system(8.1; 8.2), said system including non-return means (8.11; 8.21) causingthe working chamber concerned to close automatically during compression,and causing said chamber to open during expansion, said common chamberconstituting a compensation chamber ensuring continuity of the hydraulicfluid during displacements of the rod-and-piston assembly (2, 3) in thecylinder (4).
 2. A shock absorber according to claim 1, characterized inthat the hydraulic fluid occupying the working chambers (5.1; 5.2) isidentical to the liquid of the heterogeneous energyabsorption-dissipation structures (9, 9′).
 3. A shock absorber accordingto claim 1, characterized in that each heterogeneous energyabsorption-dissipation structure (9, 9′) is confined in a deformableleakproof housing, the hydraulic fluid occupying the working chambers(5.1; 5.2) then being a conventional engineering fluid.
 4. A shockabsorber according to any one of claims 1 to 3, characterized in thatthe rod-and-piston assembly (12; 112; 212) comprises a rod which ishollow on either side of the piston, each hollow portion defininginternally a chamber containing a heterogeneous energyabsorption-dissipation structure enclosed in a flexible leakproofenvelope.
 5. A shock absorber according to any one of claims 1 to 3,characterized in that the rod-and-piston assembly (312) comprises a rodwhich is solid on either side of the piston, and said shock absorber haschambers containing respective heterogeneous energyabsorption-dissipation structures enclosed in flexible leakproofenvelopes, which chambers are then placed around the cylinder, inside acommon housing (370).
 6. A shock absorber according to claim 4 or claim5, characterized in that the rod-and-piston assembly (12) is constitutedby tow portions (14, 15) having the same outside diameter.
 7. A shockabsorber according to claim 4 or claim 5, characterized in that therod-and-piston assembly (112; 212; 312) is constituted by two portionshaving different outside diameters, the portion with the larger diameterbeing adjacent to the structure to be protected, and the portion withthe smaller diameter being adjacent to the external source ofdisturbance.
 8. A shock absorber according to claim 4, characterized inthat each flexible leakproof envelope (50; 60) is secured to the endwall (14.2; 15.2) of the associated internal chamber (20; 21) of therod-and-piston assembly (12).
 9. A shock absorber according to claim 5,characterized in that each flexible leakproof envelope (350, 360) issecured to the inside wall of the common housing (370).
 10. A shockabsorber according to claim 5, characterized in that each flexibleleakproof envelope (350, 360) is freely suspended inside an associatedlateral housing (370.1, 370.2) rigidly secured to the central housing(370) and in communication therewith via an associated window (314.3,315.3).
 11. A shock absorber according to claim 4 or claim 5,characterized in that each flexible leakproof envelope (150, 160; 250,260) is freely suspended in the associated internal chamber of therod-and-piston assembly.
 12. A shock absorber according to any one ofclaims 1 to 11, characterized in that the capillo-porous matrices (51,61; 151, 161; 251, 261; 351, 361) are topologically and geometricallyidentical on either side of the piston, each matrix being singly-porousor multiply-porous as a function of the stiffness desired of the shockabsorber.
 13. A shock absorber according to any one of claims 1 to 11,characterized in that the capillo-porous matrices (51, 61; 151, 161;251, 261; 351, 361) are topologically and geometrically different onopposite sides of the piston, each matrix being singly-porous ormultiply-porous as a function of the stiffness desired for the shockabsorber.
 14. A shock absorber according to any one of claims 1 to 13,characterized in that the lyophobic liquids (52, 62; 152, 162; 252, 262;352, 362) have identical surface tension characteristics on either sideof the piston.
 15. A shock absorber according to any one of claims 1 to13, characterized in that the lyophobic liquids (52, 62; 152, 162; 252,262; 352, 362) have different surface tension characteristics on eitherside of the piston.
 16. A shock absorber according to any one of claims1 to 15, characterized in that the common compensation chamber (30; 130;230; 330) has a flexible wall so as to present a volume that isvariable.
 17. A shock absorber according to claims 4 and 16,characterized in that the flexible wall (31) surrounds a central portionof the cylinder (11) so as to define an annular chamber constituting thecompensation chamber (30).
 18. A shock absorber according to claims 4and 16, characterized in that the common compensation chamber (130; 230)having a flexible wall is arranged inside the piston which is designedto be hollow.
 19. A shock absorber according to claims 4 and 16,characterized in that the common compensation chamber (330) having aflexible wall is an annular chamber arranged at the end of the commonhousing (370).
 20. A shock absorber according to any one of claims 1 to15, characterized in that the common compensation chamber (7) has arigid wall, and presents an end wall (7′, 7″, 71′″) that is movable ordeformable and that is associated with a resilient member.
 21. A shockabsorber according to any one of claims 1 to 20, characterized in thatthe valve system (32; 33) associated with each working chamber includesa throttle (34; 36) defining a calibrated orifice (38; 39) for passinghydraulic fluid coming from the common compensation chamber (30).
 22. Ashock absorber according to claim 21, characterized in that eachthrottle (34; 36) is individually adjustable, and in particular can beset to a position such that the maximum value of the hydraulicresistance of said throttle corresponds to the value of the capillarypressure at which the liquid (52; 62) intrudes into the pores of theassociated matrix (51; 61).
 23. A shock absorber according to claims 1and 17, characterized in that the non-return means of the valve system(32; 33) associated with each working chamber comprises a deformableflat collar (40; 41) with two branches capable of closing radialorifices (24; 25) of the cylinder (11) which communicate via respectivechannels (22; 23) with the common compensation chamber (30).
 24. A shockabsorber according to claim 1, and claim 18 or claim 19, characterizedin that the non-return means of the valve system (132, 133; 232, 233;332, 333) associated with each working chamber comprises moving valvemembers optionally biased by associated springs.
 25. A shock absorberaccording to claim 24, characterized in that the moving valve members(232, 233) are arranged at the ends of a central tube (232′) opening outinto the hollow piston (213) via associated orifices (232″), thecompensation chamber (230) containing a toroidal bellows containing airand surrounding said tube.
 26. A shock absorber according to claim 24 orclaim 25, characterized in that the moving valve members (132, 133; 232,233; 332, 333) present respective central passages (138, 139; 238, 239;338, 339) forming calibrated orifices.